Temperature vs mpg

[duanelaugh]

After several tests at different temperatures, my '06 Prius, 1500 miles, gets 46 mpg at average temps of 95 degrees plus. However, at 75 degrees that jumps to 56 mpg. This is over a course of 40 miles, ACset at 79 degrees. Approx 50 percent on the interstate, 25 percent on rural highways and 25 percent on city streets. In my experience each 10 degrees over 75, it costs about 4 or 5 mpg. This seems more significant than even tire pressure, which I have set at 38 front and 36 psi in the rear tires.

Just for info, Duane

[berylrb]

<div class='quotetop'>QUOTE(Duane @ Aug 28 2006, 10:00 AM) [snapback]310530[/snapback]</div>

After several tests at different temperatures, my '06 Prius, 1500 miles, gets 46 mpg at average temps of 95 degrees plus. However, at 75 degrees that jumps to 56 mpg. This is over a course of 40 miles, ACset at 79 degrees. Approx 50 percent on the interstate, 25 percent on rural highways and 25 percent on city streets. In my experience each 10 degrees over 75, it costs about 4 or 5 mpg. This seems more significant than even tire pressure, which I have set at 38 front and 36 psi in the rear tires.

Just for info, Duane
[/b]

Hey Duane, welcome to PC if you havent' been already. Hey, question for ya, could this possibly be more about AC then temp? That is, if you have the AC set to 79 it wouldn't come on for your 75 degree test, whereas it would be running alot with your 95 degree parameter, eh?

Search for AC threads and I think they were talking about the same numbers 4-5 mpg running AC or not.

[efusco]

Unfortunately your numbers are a bit difficult to use due to the AC use and the variability of terrain and such.

But yes, the temps are an important factor. If you run without AC your mileage will get better as temps get higher, but the cost of running the AC tends to balance things a bit.

[richard schumacher]

<div class='quotetop'>QUOTE(efusco @ Aug 28 2006, 10:11 AM) [snapback]310538[/snapback]</div>

If you run without AC your mileage will get better as temps get higher [...]
[/b]

Up to the point that the traction battery gets too hot. If the driver can hear the battery vent fan then the battery is too warm.

[duanelaugh]

[Yes, that was my thought exactly....the AC was the additional load, maybe not so much the air temp and engine. The area I was driving was perfectly flat with only slight hills over the over passes. All the tests were over exactly the same roads. The outside air temp has been in the mid to high 90's here in the Sarasota area ever since I picked up my Prius with only ond day that it dropped to 75 degrees. The temps are from the outside air temp reading on the highway.

[eagle33199]

Also, please realize that this is a rather limited sampling, the results of which rally don't tell us much. With only 1500 miles on the car, you're still breaking it in, which means the car itself is slowly being able to get better mileage (as mechanical parts wear off the rough edges), and your driving skills for getting good MPG are slowly improving (since 99.9% of people didn't have any way of seeing realtime MPG data before owning a Prius). Additionally, there are other factors that could effect the MPG which weren't listed as being the same, such as wind conditions (tail wind versus head wind). Additionally, with only having one day that dropped down to 75, you don't have much of a basis... there could be any number of reasons to get better mileage on that one day that have nothing to do with temperature.

That being said, you can be sure that having the A/C on does drop your mileage by some degree, especially with temperatures over 90.

Unfortunately, in order to acurately test a hypothesis like the one you proposed, you'd need to get a climate controlled room (like the one the EPA uses for their mileage tests) and create identical conditions for the car (including acceleration and deceleration), with the only exception being the temperature and A/C usage... Baring that, i'd say give it a year or so to accumulate sufficient mileage data over time, then come back and see if those averaged results support the hypothesis. You might have to account for other linear trends in the data, like the break in period, in order to equalize everything.

All in all, it's a good start, and at least you have a working hypothesis to start from.

[TonyPSchaefer]

I have tracked my mileage for the last two years along with temperature. I have found that mileage per tank tracks the temperature rather predictably. Minor fluctuations are due to various thing - such as the 11-day tank driven through 9 days of rain resulting in an MPG decrease counter to the temperature increase.

Refer to the chart below. Temperature shades red to blue, the dotted line represents tank averages, and the thick pink line is lifetime average.

[berylrb]

<div class='quotetop'>QUOTE(TonyPSchaefer @ Aug 28 2006, 11:57 AM) [snapback]310592[/snapback]</div>

I have tracked my mileage for the last two years along with temperature. I have found that mileage per tank tracks the temperature rather predictably. Minor fluctuations are due to various thing - such as the 11-day tank driven through 9 days of rain resulting in an MPG decrease counter to the temperature increase.

Refer to the chart below. Temperature shades red to blue, the dotted line represents tank averages, and the thick pink line is lifetime average.
[/b]

nice graph Tony, is this detecting global warming too! LOL

so comment on AC use and your graph if you please?

[TonyPSchaefer]

<div class='quotetop'>QUOTE(berylrb @ Aug 28 2006, 11:13 PM) [snapback]310967[/snapback]</div>

nice graph Tony, is this detecting global warming too! LOL

so comment on AC use and your graph if you please? [/b]

What I point out to new drivers is the first ten months of learning curve before I posted any good numbers.

As for A/C, I use it sparingly don't shy away from it. I carpool now and my passenger pretty much insists that it be on. Of course, when it's above about 80ºF outside it's coming on anyway, but usually only enough to take the edge off the heat. Also, on a trip-bt-trip basis, I don't see a substantial MPG drop that I can attribute solely to A/C when I'm maintaining movement. The only time I can blame A/C is when I'm standing still and the A/C is pulling down the battery. But even with the A/C running, if you try to adhere to proper PnG techniques, coast when possible, stealth when possible, anticipate stops and all that other stuff, it's all good.

For the full list of tank-by-tank comments, click the link in my signature. You understand that I'm not going to recreate it all here.

[NorwoodIV]

11-day tank driven through 9 days of rain resulting in an MPG decrease counter to the temperature increase.

Refer to the chart below. Temperature shades red to blue, the dotted line represents tank averages, and the thick pink line is lifetime average.
[/quote]

Now, we need you to adjust the chart to include humidity, barometric pressure, and approximate altitude above sea level. How many passengers did you carry each time? Was the car clean? Do you have a dog? How much do you weigh? Do you tend to eat heavy meals? Did the dog eat a large meal?

You clearly are leaving way too many loose variables in your data collection and reporting. The conclusions you draw and report simply don't give the readers nearly enough information and may be misleading.

(All kidding aside, a very interesting thread...)